This invention relates to a process for selectively preparing the cis-isomer of 2,2-dimethyl-3-(2,2-dihalovinyl)cyclopropane carboxylic acid. Novel intermediates useful in the preparation of this isomer are also described.
The 2,2-dimethyl-3-(2,2-dihalovinyl)cyclopropane carboxylic acids (hereafter, DHCA) are well known compounds. These compounds are recognized to be useful intermediates in the preparation of a variety of esters having insecticidal activity.
3-(Fluorophenoxy)benzyl substituted cyclopropanecarboxylates are taught in German Pat. No. 2,547,534. 3-Phenoxybenzyl cyclopropane carboxylates are also taught in Japanese Pat. No. 76-011106. Phenoxy phenyl substituted cyclopropanecarboxylates are described in U.S. Pat. No. 3,961,070 and in South African Pat. No. 75/03,211 (based on U.S. patent application Ser. No. 487,417 filed Oct. 7, 1974). Other related substituted phenyl esters of cyclopropane carboxylic acids are taught in French Pat. No. 2,281,918. Various insecticidal 3-(dihalovinyloxy)benzyl esters of cyclopropanecarboxylic acid are taught in German Pat. No. 2,554,883. In addition, U.S. Pat. No. 3,979,519 teaches the use of 3-(2,2-dihalovinyloxy)benzyl 2-(2,2-dihalovinyl)3,3-dialkylcyclopropane carboxylates as insecticides. Additional esters of DHCA are described in U.S. Pat. Nos. 4,281,133, 4,301,154, 4,256,893, 4,332,815 and 4,163,787. The relevant portions of all of the aforementioned patents are incorporated herein by reference.
The dihalovinyl moiety and carboxylic acid group present on adjacent carbons of the cyclopropane of DHCA can be disposed in cis- or trans-isomeric forms. It is known that certain insecticides prepared from DHCA exhibit increased insecticidal activity relative to certain target species where present as the cis-isomer rather than the trans-isomer or a mixture of isomers. See, Synthetic Pyrethroids, ACS Symposium Series 42, p. 53 (1977). Accordingly, techniques for selectively preparing the cis-isomer of DHCA are of considerable interest.